Among fully vaccinated Covid-19 infections, breakthroughs are more common than previously thought: does it matter?

Vaccines are very effective in preventing serious illness from Covid-19, but they do not form a “golden shield” against contracting the coronavirus.

In recent days, revolutionary infections have featured prominently in the news. On Tuesday, the White House announced major infections among fully vaccinated staff. Breakthroughs have also taken place on Capitol Hill. For example, a number of people vaccinated in President Pelosi’s office have tested positive. And the Covid-19 epidemics continue to wreak havoc in the world of professional sports, including several cases among vaccinated New York Yankee baseball players.

Breakthrough infections are more common than previously thought, and their incidence likely increases with the ancestry and maintaining the dominance of the Delta variant.

The question is, does it matter? The answer is yes. First, although breakthrough infections usually don’t lead to serious illness, they can. In the UK, it was reported two days ago that 40% of confirmed Delta variant patients admitted to hospital had received at least one dose of the vaccine. This implies at least moderate resistance to the vaccine, especially in those who have only one dose. Second, and this is important in terms of viral spread, vaccinated people who contract breakthrough Delta variant infections can and do transmit the coronavirus to others.

Virologists at several of the Netherlands’ leading academic medical centers have observed that fully vaccinated healthcare workers who contract the coronavirus can transmit it, whether symptomatic or asymptomatic. Transmission can occur from fully vaccinated people to partially and unvaccinated people, but also between fully vaccinated people. Therefore, the implications of breakthrough infections for further transmission are quite obvious. Although Dutch virologists recognize that most of the source of the virus’s spread is among the unvaccinated, it is clearly not limited to this group.

As such, the Delta variant presents a formidable challenge. MRNA and other vaccines are still resistant to serious disease, but not so good at preventing infection.

This week, Israel reported an efficacy rate of the vaccine of between 88% and 91% against the Delta variant in preventing serious illness; a decrease, albeit relatively modest, from the initial figures reported four months ago. But, it seems that there is a much more important reduction in effectiveness against infection prevention; a decrease of more than 50%, which is consistent with the theme of decreasing the effectiveness of the vaccine over time, as shown in a study previously published by the Israeli Ministry of Health and in studies from the UK Kingdom and Singapore.

Asked Wednesday evening about the revolutionary cases of Covid-19, President Biden responded by saying that it was a “tiny percentage and not a danger to life”. The media mainly approve of this rather categorical view which is incompatible with the data. For example, the New York Times published an article Thursday claiming breakthrough infections were “relatively rare.”

Well, breakthrough infections are actually not uncommon.

According to the Dutch RIVM (CDC counterpart in the Netherlands), 9% of all positive cases in the Netherlands last week were fully vaccinated individuals, and 14% of positive cases were partially vaccinated individuals.

Dutch virologists who have observed fully vaccinated healthcare workers contract coronavirus and then pass it on to others, point out that their findings may be relevant in terms of formulating a masking and distancing policy for those vaccinated in indoor public spaces.

The White House is currently debating whether to reinstate guidelines that urge indoor masking for the vaccinated as well as the unvaccinated. At the same time, President Biden and the director of the Centers for Disease Control and Prevention, Dr Walensky, say that masking for the vaccinated is a “personal choice.” This suggests that unequivocal guidelines on masking are not available.

In the absence of an unambiguous federal policy, a patchwork of local and state policies will continue to emerge. A number of municipalities have already reinstated mask-wearing mandates that apply to everyone, whether unvaccinated, partially or fully vaccinated. Others may follow suit as the Delta wave intensifies.