Israeli Study Shows A Majority Of Those Vaccinated Can Be Infected By SARS-CoV-2
(Posted on Wednesday, January 27, 2021)
As vaccine distribution is picking up with nearly 70 million doses administered worldwide, data regarding large-scale vaccination is becoming available. Last week, Israel released preliminary data on the effects of vaccination for infection. Early indications suggest that after vaccination, as many as 70% of people can still be infected. More data is needed to confirm the effects on transmissibility among the vaccinated.
Israel, which leads the world in vaccinations per capita at around 43 doses per 100 people, developed this study to understand how the Pfizer-BioNTech vaccine affects viral infection. Previous studies show the vaccine is effective in preventing Covid-19 related mild and severe symptoms. While the Covid-19 vaccines are intended to protect a patient from symptoms, having your shots doesn’t necessarily mean you can’t still be infected by SARS-CoV-2 or spread it to others.
The study contrasted a group of 200,000 vaccine recipients aged 60 and above with a group of 200,000 who hadn’t been vaccinated in the same age group. To quote the Clalit website:
“The study showed that between the fifth day and the 12th day after receiving the first vaccine dose, there were no differences between the vaccinated group and the non-vaccinated group: the rate of positive tests for the SARS-CoV-2 in the two groups was similar. In other words: no difference in infection rates was observed between those who were vaccinated and those who were not vaccinated.”
The report continued “that 14 days after the injection of the first vaccine, there is a real decrease in the rate of infection in the SARS-CoV-2.” 17 days after the initial dose of the vaccine, between 60 and 80% of people can still be infected.
The release of this data is a positive development. For months, the impact of vaccines on the pandemic has been mostly speculative. Nobody knew how mass vaccination might affect infectability or transmissibility. This data is the first of many, and we await data from similar studies.
While data remains limited on the transmissibility of the vaccinated, it may be the case that it is reduced among most. If neutralizing antibodies from the vaccines do their jobs, the viral load in a person infected with SARS-CoV-2 is much lower than in those who haven’t been vaccinated. A lower viral load may mean that they are less likely to infect others with the same efficiency that an unvaccinated person may. The vaccinated patient has less virus in them to spread around. Though we don’t know whether this is the case, more data is needed to know if those vaccinated and infected can transmit the virus to others.
After the first dose, more than 50% of people remain at risk of infection. Vaccine protection from disease, but not infection, is observed for other respiratory viruses. The flu vaccine, for example, does not typically protect people from infection and further transmission, but only symptoms. Flu vaccines typically reduce risk by 40-60%, meaning receiving a flu shot won’t guarantee you protection from influenza infection.
The question of transmissibility is more complicated. Some studies have been conducted on guinea pigs for influenza, showing a moderate reduction in influenza transmissibility from vaccinated hosts. Infection in those vaccinated may be a consequence of the short duration of the IgM and IgA antibodies active at mucosal surfaces, especially the nasal mucosa. Both IgM and IgA antibodies vanish after 4-5 weeks post-induction. The longer-acting IgG antibodies are very likely key to reducing disease severity but are unlikely to prevent infection via the nasal mucosa or other mucosal surfaces.
Emerging SARS-CoV-2 variants throw another spanner in the works. New variants have shown to be more aggressively transmissible. Some studies have even indicated that certain variants evade immune-responses from naturally occurring or even vaccine antibodies. If this is the case, a vaccinated community may be ravaged by a variant. Such variants have the potential to infect and sicken even those who have been vaccinated. A recent study from Chongqing China shows that sera from those infected by the original Wuhan strain in January and February of last year have little to no ability to protect against either the UK (B.1.1.7) the South African (B.1.351) strains.
Ultimately, we need more data. This study is preliminary, and the results may not be completely indicative of global infectivity rates post-infection. As more countries continue to vaccinate in higher quantities, we will know important information like efficacy, transmissibility, infection among the vaccinated, and more. That information will roll in slowly but surely in the coming weeks.
Originally published on January 27, 2021.
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