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Disinformation Raises Concerns
The existence of the pandemic was an easy, but decidedly late, call. A flu pandemic is simply a novel strain that spreads worldwide. The detection of swine H1N1 in two children in southern California in March/April strongly suggested that the pandemic had begun. The children had no contact with swine or each other and were over 100 miles apart, indicating the detected infections represented thousands of cases in southern California, including symptomatic relatives and contacts. When the “mystery illness” that was hospitalizing and killing 100’s in Mexico was confirmed in April to be the same swine H1N1, it was clear that the pandemic had begun. The original phase 6 definition of sustained transmission of a novel strain of influenza had been met.
The swine H1N1 contained flu genes that had been circulating in swine since the 1990’s and most of the flu genes had been in swine since the 1930’s or earlier. Thus, the H1N1 was novel and the vast majority of the world’s population had no immunity, setting the stage for rapid spread worldwide. Although jumps of swine H1N1 to humans happen multiple times per year, prior jumps generally had a direct link to swine exposure and transmission was limited to family members of close contacts. The most extensive spread was in 1976 at Fort Dix in NJ where one soldier died and 200 were infected. However, the virus did not spread outside of Fort Dix and was quickly contained.
In contrast, the 2009 pandemic strain had already been detected in TX, KS, and NY by the time H1N1 from Mexico was confirmed by the US and Canada, so the viral transmission was sustained in North America. Moreover, symptoms in 150 students in one high school in Queens, NY indicated the attack rate was high and global spread had already happened, but had not yet been detected / reported.
The updated phase definitions required sustained transmission in one large area, like the Americas, for phase 5, which had also been met, while phase 6 required sustained transmission in multiple large areas, which was met as soon as widespread H1N1 was reported in Australia or UK, but the announcement was delayed until community spread in these areas was documented many times over.
Thus, when phase 6 was declared, the pandemic was well underway.
Flu pandemics typically happen in multiple waves. Although the new virus persists for years or decades, the severity of the virus is generally highest in the first several years, as the virus adapts to its new host. Initially, the virus can quickly spread because of a large naïve population. This initial wave can be mild because low levels of virus can produce successful infections and transmission. Thus, although some immunity may quickly develop in a large segment of the population, this immunity may not prevent re-infections.
In one of the initial vaccine trials in Australia, 31% of volunteers had H1N1 antibody titers of 40 or higher, indicating they had been previously infected, even though they denied such infections. Moreover, the vaccination led to higher titers in the vast majority of these patients, indicating initial infections produce a sub-optimal level of immunity. However, this level may be sufficiently high to end a wave, but not sufficiently high to prevent a new wave by a virus that is either circulating at higher levels or has relatively minor genetic changes, leading to multiple waves within one season.
This season there was an early wave, which could be considered a second wave, or just an extension of the spring wave.
However, in either event, the potential for another wave in the winter/spring is high, because conditions support the spread of influenza, and the pandemic H1N1 has crowded out seasonal H1N1 and H3N2, so the only influenza A currently circulating at significant numbers is pandemic H1N1.
In the latest CDC report (week 4), region 4 had a significant increase in the frequency of H1N1 detection in tested samples to levels that had not been seen since November, when the earlier wave was ending.
Thus, declarations of the end of the 2009 pandemic are premature, and the absence of seasonal H1N1 and H3N2 indicate the swine H1N1 will persist for years or decades, as happened with new serotypes responsible for earlier influenza pandemics. The current pandemic has already spread worldwide, so calling it an epidemic is incorrect, but such terminology has become widespread in recent media reports.
This expanding disinformation on the current pandemic is of concern and is hazardous to the world’s health.