(Bloomberg) — After the first vaccines against Covid-19 demonstrated efficacy, public health officials began to foresee a gradual end to the pandemic. Getting there with a minimum of additional suffering will require widespread inoculation, with the goal of achieving so-called herd immunity. Health specialists warn that vaccine hesitancy — a reluctance to accept immunization — threatens to undermine that target and could mean deaths from Covid are several times higher over coming years in countries with lower rates of acceptance than in those with a high uptake of vaccines.
1. How much hesitancy exists around Covid vaccines?
Hesitancy increased in the European Union after several countries in the bloc suspended use of AstraZeneca Plc’s vaccine because of concerns about blood clots. In an online survey conducted in April by Eurofound, 34% of respondents indicated they were unlikely to get immunized against Covid. Before the AstraZeneca pause, the figure was 25%. Skepticism was highest in Bulgaria, at 61%, and below 10% in Denmark, Malta and Ireland. According to U.S. census data as of late April, 12% of American adults were hesitant about getting a Covid vaccine, with the rate ranging considerably by state, going as high as 26% in Wyoming. In a survey across 19 countries in June 2020, before Covid vaccines became available, 72% of people said they would take a shot that proved safe and effective. The acceptance rate ranged widely among countries, from 55% in Russia to 89% in China. In an article in Nature Medicine, researchers wrote that in most of the countries, there was insufficient willingness to accept a Covid vaccine to meet the requirements for herd immunity.
2. What explains hesitancy around Covid vaccines?
A number of reasons. Some people don’t think the threat of Covid justifies getting a vaccine and risking side effects, particularly if they live in an area with a low rate of cases; this means it may grow harder to persuade the last holdouts as vaccination coverage increases and cases drop. The unprecedented speed with which the shots were developed and granted emergency authorization also spurred questions about whether they could be harmful and if the process was influenced by political leaders, jeopardizing its integrity. Some people want others to go first and assume the risk. Finally, there are the efforts of anti-vaccination campaigners, who have spread disinformation about Covid and the vaccine effort from the start.
3. What is herd immunity?
When a large portion of a community (“the herd”) is immune to a disease after falling ill or being vaccinated, it becomes much more difficult for the virus to jump from one person to the next as it’s harder to find a vulnerable host. The pathogen’s transmission slows and eventually stops, until it dies out within the community. As a result, the whole group becomes protected, not just those who are immune.
4. What are the requirements for herd immunity?
There’s a fair bit of math and considerable uncertainty involved. The percentage of people who must be immune depends on how contagious a pathogen is. In a November paper in the medical journal The Lancet, researchers calculated that a vaccine that provides lifelong, 100% protection against infection with SARS-CoV-2, the coronavirus that causes Covid, would need to reach 60% to 72% of people.
5. Will Covid vaccines provide that?
No. In clinical trials, the Covid vaccines in use around the world proved effective in preventing people from getting sick with Covid, not necessarily from getting a low-level coronavirus infection that could be passed on. Their efficacy rates against disease varied from 95% — for two of them, one from Pfizer Inc. and BioNTech SE and another from Moderna Inc. — to 50% — for a vaccine from China’s Sinovac Biotech Ltd, which has shown much greater efficacy in preventing hospitalization in an initial real-world trial. In Israel, which has one of the world’s highest rates of Covid vaccination, the effectiveness of the Pfizer-BioNTech vaccine at preventing asymptomatic infection was estimated at 91.5%, but further studies are needed to confirm that result and determine the figure for other vaccines. If the vaccines prove to be 80% effective at preventing infection, 75% to 90% of people would need to be immunized, according to the Lancet paper. Another unknown is exactly how long vaccine protection lasts, though some scientists are confident that immunity after recovery from a case of Covid lasts as long as eight months, which could be similar for vaccines. The shorter the duration, the higher the rates of immunization required to establish herd immunity.
6. What about people who have immunity because they’ve been infected?
It’s possible that a vaccine might not have to do all the work to get to herd immunity. Some people will have immunity because they’ve already had the virus. A study in September, before vaccines became available, concluded that about 9% of people in the U.S. had antibodies to the virus and so, presumably, some level of protection.
7. What if herd immunity isn’t achieved?
One scenario is that some places might get to herd immunity and thus stop transmission of the virus, while in other places it would become endemic — that is, continuously circulating with periodic spikes when conditions favor transmission. David Heymann, chair of the World Health Organization’s strategic and technical advisory group for infectious hazards, warned at the end of 2020 that “it appears the destiny of SARS-CoV-2 is to become endemic.” In an analysis published in March, Imperial College London estimated that, based on current levels of skepticism about the shots, France could see 8.7 times more deaths in the next two years than it would under the ideal level of uptake — where 98% of individuals ages 15 and over are vaccinated. The figures for Germany and the U.K. were 4.5 and 1.3 respectively. Overall, the authors estimated that even modest levels of hesitancy could lead to an extra 236 deaths per million people over a two-year period, assuming the vaccines administered have an efficacy of 94%.
8. What are the risks of Covid vaccines?
Like all new pharmaceuticals, the vaccines that have been authorized to protect against Covid come with some safety concerns and side effects. Many people who’ve received the shots have experienced fever, headache and pain at the site of the injection. These side effects generally disappear quickly. So far, vaccines have been connected to a relatively small number of cases of blood clots and serious, but treatable allergic reactions called anaphylaxis. Other concerns, about vaccinations causing a temporary facial paralysis or weakness known as Bell’s palsy and otherwise unexplained deaths, have not proven justified.
9. How are such cases monitored?
In the U.S., health workers are observing everyone who receives a Covid vaccine for at least 15 minutes to watch for signs of a reaction; those with a worrying history of allergic reaction are monitored for twice as long. Most advanced countries have established systems for reporting adverse side effects of vaccines. In the U.S., anyone can submit a report to the Vaccine Adverse Event Reporting System, which serves as an early warning system to identify side effects. The U.K. has a similar program, called the Yellow Card Scheme. In addition, U.S. authorities have created a system using text messaging and web surveys to check in with Covid vaccine recipients. Vaccine manufacturers are establishing their own means to monitor side effects. Pfizer-BioNTech has announced plans for three studies following people post-vaccination for 30 months.